The present invention relates to an elastomer delustering method and more particularly to a method for efficiently delustering an elastomer that either is initially devoid of delustering properties or has inadequate delustering properties.
Examples of methods for forming delusterant elastomers include methods for curing silicone elastomer compositions containing delustering inorganic fillers and methods for curing silicone elastomer compositions containing organic compounds having air-oxidizable/curable unsaturated groups as disclosed in Japanese Patent Application Laying Open No. 2000-80276 and 2000-86896.
In addition, a surface roughening technique such as that proposed in Japanese Patent Application Laying Open No. Hei 6-269727 and a technique for applying delustering coatings having glass spherules such as that proposed in Japanese Patent Application Laying Open No. Hei 8-57410 are known as methods for improving the delustering properties of such elastomers or imparting delustering properties to elastomers originally devoid of delustering properties.
However, the techniques disclosed in Japanese Patent Application Laying Open No. Hei 6-269727 and 8-57410 are disadvantageous in that the appearance of the elastomer surface is adversely affected or that the newly formed delustering coatings peel off because of inadequate affinity for the elastomers.
Specifically, an object of the present invention is to provide a method for efficiently delustering an elastomer that either is initially devoid of delustering properties or has inadequate delustering properties.
The present invention is an elastomer delustering method comprising impregnating the surface of an elastomer with an organic compound having air-oxidizable curable unsaturated groups.
The present invention is an elastomer delustering method comprising impregnating the surface of an elastomer with an organic compound having air-oxidizable curable unsaturated groups. The elastomer used in the present method can be any rubber or gel product that can be impregnated with an organic compound having air-oxidizable and/or curable unsaturated groups or a solution thereof. Specific examples of such elastomers include EPDM, butyl rubber, polybutadiene rubber, fluororubber, polyurethane, silicone rubber, and silicone gel, of which silicone rubber and silicone gel are preferred. The silicone rubber and silicone gel used herein are not limited in any way and include products obtained by curing silicone compositions of the addition reaction curing type, products obtained by curing silicone compositions of the condensation reaction curing type, products obtained by curing silicone compositions of the addition reaction and condensation reaction curing type, products obtained by curing silicone compositions of the peroxide curing type, and products obtained by curing silicone compositions of the UV curing type. In particular, surface adhesion can be reduced when silicone gel elastomers are used.
The organic compound having air-oxidizable curable unsaturated groups that is used in accordance with the present method is a component designed to impregnate and deluster the elastomer surface. The organic compound is one in which the unsaturated groups in the molecules are cured by the oxygen in air. Specific examples include linolenic acid, linolic acid, and other unsaturated higher fatty acids; tung oil, linseed oil, soybean oil, and other oils and fats consisting of esters of glycerin and unsaturated higher fatty acids; methyl linolenate, methyl linoleate, and other esters of alcohols with unsaturated higher fatty acids; and butadiene, pentadiene, hexadiene, 2,6-dimethyl-2,4,6-octatriene, and other unsaturated hydrocarbon compounds or polymers thereof, of which linolenic acid, methyl linolenate, tung oil, 1,3-hexadiene, 1,4-polybutadiene, and 2,6-dimethyl-2,4,6-octatriene are preferred.
Although using an organic solvent in the present method is optional, such use becomes obligatory when, for example, the elastomer surface is difficult to impregnate using the organic compound as such. In such case, a solution containing 1 to 10 wt % of the organic compound should preferably be prepared. Any organic solvent capable of causing elastomer swelling can be used. Examples include hexane, heptane, octane, decane, and other aliphatic hydrocarbons; toluene, xylene, and other aromatic hydrocarbons; ethyl acetate, butyl acetate, and other esters; THF and other ethers; chloroform, carbon tetrachloride, dichloromethane, and other halogenated hydrocarbons; and low-viscosity silicone oils such as dimethylsiloxane oligomers (e. g. hexamethyldisiloxane and octamethyltrisiloxane) and cyclic dimethylsiloxanes (e.g. octamethylcyclotrisiloxane, tetramethylcyclotetrasiloxane, tetramethyltetravinylcyclotetrasiloxane, and decamethylcyclopentasiloxane); as well as gasoline and rubber naphtha.
Antioxidants such as hydroquinone and eugenol and curing accelerators such as cobalt naphthenate, lead naphthenate, and manganese naphthenate can be optionally used together with the aforementioned organic compounds in the present method.
Examples of techniques for impregnating an elastomer surface with an organic compound having air-oxidizable curable unsaturated groups include techniques in which the elastomer is immersed in the organic compound or a solution thereof, techniques in which the elastomer is sprayed with the organic compound or a solution thereof, and techniques in which the organic compound or a solution thereof is applied to the elastomer with a brush. The amounts used for the treatment are not limited in any way and is selected such that the elastomer surface is impregnated with the organic compound and provided with adequate delustering properties. Any organic compound or organic compound solution remaining on the elastomer surface should preferably be washed away with an organic solvent and wiped off with paper or the like.
According to the present method the elastomer surface can be delustered by a technique in which the elastomer treated with the organic compound is held or heated in the presence of oxygen, specifically in air. To adequately deluster the elastomer surface it is preferable to adopt an approach in which the elastomer is allowed to stand, for example, for 3 to 7 days in air at room temperature.
With the method of the present invention it is possible to impart adequate delustering properties to an elastomer initially devoid of delustering properties or an elastomer whose delustering properties are below expectations. This method is therefore useful for making elastomers more aesthetically appealing or improving the quality of delustered elastomers. This method is also useful as a detackifying technique because it reduces the surface adhesion of gel-like elastomers.
The present elastomer delustering method will now be described in further detail through working examples. In the working examples, viscosity is a value obtained at 25xc2x0 C. The delustering properties of an elastomer were evaluated by measuring the glossiness of the elastomer by the glossiness measuring method defined in JIS Z 8741 (measurement angle=60xc2x0).